Police want to speak to this man over the incident (Picture: British Transport Police)

Police are hunting for this man after a woman was sexually assaulted for 40 minutes while she slept on a train.

The woman, 33, was heading to Clacton from Liverpool Street Station, London, when she was assaulted.

British Transport Police are investigating the incident which happened on Friday, November 14, at around 9.38pm.

Detective Constable Alan Reed said: ‘A 33-year-old woman was approached by a man on the platform at Liverpool Street, as she prepared to board her train. The man subsequently joined her on the service.’

During the journey she fell asleep only to be awoken by the male touching her inappropriately.

On arrival at Witham the man got off the train.

DC Reed said: ‘I am confident the man in the image we are issuing today can help with our investigation. Who is he?’

Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference ESUB/B6 of 17/12/2014. Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.